At present, a 3rd Generation Partnership Project (3GPP) proposes a concept of LTE Assisted Access (LAA) to use unlicensed spectrum with help of Long Term Evolution (LTE) licensed spectrum. When using unlicensed frequency bands, LTE networks need to ensure that an LAA system can coexist with related access technologies such as Wi-Fi access technologies on a fair and friendly basis. However, in a traditional LTE system, there is no Listen Before Talk (LBT) mechanism to avoid collision. In order to coexist with Wi-Fi, the LTE system needs an LBT mechanism. In this way, if LTE detects that a channel is busy on the unlicensed spectrum, the frequency band thereof cannot be occupied. If it is detected that the channel is idle, the frequency band can be occupied.
Traditionally, in a Physical Random Access Channel (PRACH) resource configuration of Time Division Duplexing (TDD), there are five formats of random access preamble sequences.
When the unlicensed spectrum is used in a TDD mode, an uplink/downlink configuration of a traditional TDD is fixed, such as seven kinds of fixed subframe allocation modes in the related art, so that ratio of uplink/downlink time slots is lack of flexibility.
In order to better adapt to dynamic changes of uplink/downlink services and the LBT mechanism, for example, when data is transmitted through a Physical Downlink Shared Channel (PDSCH), maximum channel occupation time of downlink may be 8 ms or 10 ms, but if a conversion from a downlink subframe to an uplink subframe is performed during this time period, an LBT channel detection must be performed again, so that the channel is taken away by other systems, such as a Wi-Fi system. In the related art, it is proposed a fully dynamic uplink/downlink subframe configuration, i.e., each subframe can be changed to an uplink subframe or a downlink subframe at any time.
However, there may be only one uplink subframe or Uplink Pilot Timeslot (UpPTS) within a frame of 10 ms, or there may even be no uplink subframe or UpPTS. In this way, it urgently needs to solve a technical problem on how to properly configure time-frequency resources occupied by the PRACH.